Electrodeposition of indium and its alloys



Patented Jan. 11,1949

ELECTRODEPOSITION OF INDIUM AND ITS ALLOYS John Robert Dyer, Jr., andTimothy J. Rowan,

Utica, N. Y., assignors to The Indium Corporation of America, New York,N. Y., a corporation of New York No Drawing. Application April 19, 1944,Serial No. 531,818

9 Claims.

This invention relates to the art of electrodeposition and particularlyto compositions, baths, and processes for the electro-deposition ofindium. In certain of its more specific aspects it relates to thee'lectro-deposition of indium together with another metal, and'incertain of its broader aspects it relates to the joint deposition of aplurality of metals.

Although indium can be deposited from various of its salts byelectrolytic action, difficulties are experienced in practice which makemost of such salts unsuitable for electro-plating of commercialarticles. In ordinary practice a bath composed of indium cyanidesolution with various addition agents has been used to the exclusion ofothers. Even this bath, however, is unsatisfactory in several respects,especially in the poisonous character of the salt and the fact that thebath becomes dark and opaque so that one cannot see the work during theplating operation.

It is, therefore, one object of the invention to provide a better bathand plating process which will be' free from these objections. It is anobject to provide for the plating of indium without the use of highlypoisonous chemicals. It is an object of the invention to provide aplating bath and process by which the bath may be kept clear andtransparent so that the work can be kept under observation at all times.It is also an object of the invention to provide a plating bath andmethod which will take indium from metallic anodes and deposit it on thearticles being plated without substantial deterioration of the bath.Another object is to provide a plating bath which, although capable ofplating indium through the bath from anode to cathode, will not dissolvethe anodes when they are left in the bath without passage of current.Another object is to provide a bath and process for plating indium whichhas good throwing power, gives a dense electro-plate of high quality andin general meets the requirements of commercial use. Still anotherobject is to provide a bath and method well adapted to co-deposition ofindium with other metals. Another object of the invention is to providea composition which can be prepared under fully controlled conditions ofchemical manufacture and furnished to platers for making of baths bysimple mixing with water, whereby to eliminate many sources of troubledue to improper composition of plating baths.

In accordance with the invention, these objects are achieved by use ofcompositions for the plating which forms an anion in the bath fortransferring the indium from anode to the articles being plated at thecathode. The bath should be kept at room temperature to avoid excessivehydrolysis of the sulfamic acid. It should be maintained at a pH belowabout 3.5 and should not exceed 3.8 at the outside unless certainaddition agents are present. Suificient sulfamate ion should be presentto carry the indium, but other anions compatible with the variousingredients of the bath may be present. This permits the supplying ofindium to the starting composition in any of a variety of compounds.

The indium may be introduced into the bath or bath-forming compositionin the form of the hydroxide or any salt of which the anion would not beincompatible with other ingredients of the bath and would notobjectionably attack the anodes or cathodes. It may, for example, beintroduced as indium sulfam'ate, chloride, bromide, sulfate, etc. If thecomposition is to be. stored or packaged dry, the hygroscopic saltsshould be avoided. In such case indium sulfamate or other salt of anorganic acid, e. g. indium carbonate, indium acetate, indium formate,can be used. It is likewise possible to use acids other than sulfamicacid for pH control.

The concentration of the indium sulfamate may be widely varied. For bestresults the concentration of indium (expressed as equivalent weight ofindium metal regardless of the particular salt used) should be about 20to grams per liter, with the optimum about 30 grams per liter. As muchas 130 and as little as 10 grams per liter, however, will give aneffective plating. The use of certain organic acids, or their salts, forexample, malic acid, alkali malates, alkali tartrates, or tartaric acid,holds the indium in solution if the conditions in the bath are such asto cause incipient precipitation. With proper concentration of theseorganic acids or salts in the bath it may be operated at pH valuesranging from 0-7 or above the normal precipitating point for indiumhydroxide. The concentration of sulfamate ion (expressed as equivalentweight of sulfamic acid whether present as acid, salt or ion) should forbest results be about 167 grams per liter, with the optimum for ordinarycommercial conditions about 226 grams per liter. As much as 760 and aslittle as grams per liter may be present and still give a useful platingof indium. The presence of other anions, e. g. Cl, Br, S04, etc.,insofar as they are not inconsistent with other ingredients of the bath,do not adversely affect the plating bath.

The indium may also be supplied initially to a strongly acid bathdirectly from an indium-containing anode by passing a current throughthe bath from an indium anode. It is better, however, to use acomposition which provides indium ions immediately. In any case, theamount of indium deposited from the bath by electrolysis will beeifectively replaced from such an anode during a plating operation; and'efficiencies at both cathode and anode of approximately 100% areattainable in practice by this invention. The anode may be indium, or amixture or alloy of indium and one or more other metals such, forexample, as lead, zinc, copper, cadmium, tin, silver, gold; or an indiumanode and an anode or anodes of one or more said metals may be employedjointly.

Various sources of SO3NH2 are satisfactory, among them, 'sulfamic acid,indium sulfamate, sodium sulfamate, potassium sulfamate, ammoniumsulfamate, aluminum suliamate, and, in general, sulfamates of metalshigher in the E. M. P. series than indium.

Addition agentsmay be used, as well understood in the art ofelectro-plating. It is particularly advantageous to use addition salts,especially sodium sulfamate, and various organic compounds, especiallynitrogen-containin compounds such as amines, which form heavy complexeswith metals, such, for example, as triethanolamine, ethanolamine,diethanolamine. Dextrose and other saccharides may be used withadvantage in the baths of our presentinvention. Triethanolamine anddextrose in particular are effective to improve the throwing power ofthe bath and the fineness and density of the deposit, Too much of theselatter .agents, however, has been found to increase the tendency togassing. Wetting agents improve throwing power, but many of the commonwetting agents so far reduce the rate of deposition as to be regarded asobjecl tionable. The use of addition salts, especially the alkalimetal(including ammonium) salts improve'the throwing power, giving a moreregular deposit, and byincreasing the available ions may facilitateco-deposition of metals where one has greater affinity "for thesulfamate ions than the other,

A composition such as contemplated by the invention is normally utilizedin aqueous solution,

but can be used in other ionizing solvents, e. g.

the lower acid amides. It is an important feature of this invention,however, that all of the ingredients of the bath except the solvent canbe furnished in dry form as a commercial product, which can be mixedwith solvent by unskilled help, and the proper specific gravity can bequickly checked with a hydrometer. When the bath is to be thus sold as adry composition, it is-advantageous to avoid hygroscopic compounds;

and since most of the indium salts of inorganic acids are hygroscopic,there is an important advantage in the use of indium sulfamate as suchin the dry composition.

Indium sulfamate, when used, provides both SOz'NI-Iz ions and theinitial In ions in the bath.

4 such addition agents as malate's, etc., to use excess sulfamic acid togive such pH, especially Where a dry composition is furnished and whereone is co-plating with lead, silver or other metal which would beprecipitated or attacked by other acids; but the use of other acidssuch, for example, as hydrochloric, hydrobromic, sulfuric, etc, issatisfactory in other cases, is within the scope of the invention, andhas some distinct advantage.

The composition of our invention may be first assembled in the bath(with the ingredients more or less ionized); or it may be provided as aconcentrate solution to be diluted for use, or it may be packaged anddistributed as a dry composition to be dissolved in an appropriateamount of water for making up the plating bath.

As an example of this invention, a plating bath embodying our inventionmay be prepared by dissolving gm. of NaOH in 700 cc. of water, coolingand adding slowly with stirring 207 gms. HSO3NH2 being careful to avoidoverheating. To this solution add 57.8 gms. InCla (equivalent to about30 gms. indium metal). This may be added as a slightly acidaqueoussolution of II1CI3 of the concentration 1:05 grams InCla per ml. liter.To this solution is then added "2 cc. triethanolamine and 8 gramsdextrose. Water is then added to make a total volume of one liter andthe resulting solution stirred thoroughly to effect complete solutionand mixing .of allconstituents. The thus combined solution is filteredand is ready for use as a plating bath. For any required volume of baththe amountsgiven above are all multiplied by the number 'of liters ofbath required.

The resulting'bath contains indium trichloride, hydrochloric acid,indium sulfamate, sulfamic acid, sodium chloride, sodium sulfamate, andthe various ions all in equilibrium.

Due to varying amounts of free hydrochloric acid in the indium chloride,the baths made up in this way from commercial materials may haveslightly different pH values. With the proportions-set forth inthe-above example pH values a. may mange from L0 to 1.5, however, pH isnot critical in this range, which seems to be an optimum range.

A 2-liter bath of "the above composition which tested pH 144, was usedto immerse an indium ano'oleanda copper cathode, each having an area of20-sq. in. A current/of 1 amp. was passed through the bath "15 hours atroom temperature,

, after which the cathode showed again of 21.138

gm. or 2-3.48*mg./amp. min. The anode showed a loss of 22.0244 pgm. or24.47 -mg./'amp. min.

The differencein cathode gain and anode loss is accounted for byinsoluble sediment from the anode. There is no sludging of the bath topor bottom andno apparent break-down of the addition agents. Anydifficulty with sedimentation may be overcome, if necessary, byenclosing the anode in a parchment or cloth bag.

The indium plating on the cathode was very dense "and smooth and therewas only slight burring at the edges.

Thebathwas then filtered and re-rated. Sue-- cessive tests showed'therate of'deposition to be 23.5 to '2316; "Successive tests on copper,indium, and lead cathodesgave rates of 23,235 and 23.6 mg.'/amp. min,respectively. The efficiency of r this bath therefore is approximately99%.

Throwing power was tested in a cell using a copper cathode "2" x 5" inthe form of a cylinder whichwas plated ati'? amp. for '10 min. Thethrowing power compared very favorably with -e fficient when in use.

.that of indium cyanide baths, and was far superior to other acid typeindium baths.

Indium anodes used with this loath are not appreciably attacked whenidle, and are nearly 100% Agitation of the bath is desirable, but notessential. Gassing may be overcome by agitation, thorough cleaning(electrolytic) of the cathode, or by flashing for a few seconds at lowcurrent density before raising the current density to the desired rate.If bubbles are allowed to form at high current density and cling to thecathode, they would leave unplated spots. After a flash of indium hasbeen de-- posited, the bubbles do not cling to the piece, and verylittle gassing occurs even at relatively high current densities. Acoating of lead hasa similar' deterrent effect on gassing. 1

Current densities ranging up to 100 amp. per square foot givesatisfactory results. 20 amp. per sq. it. has given optimum resultsunder ordinary plating conditions.

Although in commercial practice addition agents will ordinarily be used,a good plating with indium can be obtained by a simple solution ofindium sulfamate with excess sulfamic acid and with or without otherions remaining from production of the bath. As one example of thisindium chloride may be added to strong aqua ammonia in proportion of 1mol. of the indium chloride to 3 mols. of ammonium hydroxide, and tothis is added with stirring 3 mols. of sulfarnic acid. The chloride ionseems to aid the solution of the indium hydroxide precipitate and servesas part of the excess acid to maintain the required acidity in theplating bath.

The resulting solution may be packaged and distributed as a concentratewhich when diluted to a desired concentration, e. g., to 130 or even 10grams per liter of indium, can be used effectively for plating indiumfrom indium anodes.

Instead of aqua ammonia, other alkali metal hydroxides may be usedespecially sodium hydroxide or potassium hydroxide.

A similar bath may be made Without the addition of the alkali, merelyadding three mols. of sulfamic acid for each mol. of indium chlorideeither in concentrated solution for distribution or in a dilutionsuitable for the actual plating bath. ,All products of the reaction maybe left in solution.

Such a bath of 30 gm. per liter strength gives approximately 100% anodeand cathode eificiencies, no sludging at the anode and no substantialdissolution of the anode when standing in the idle bath. The pH of thebath as first made is, for example, in a particular case usingcommercial chemicals, 2.45 and after plating for 10 hours at 10 amps.per square foot was pH 2.5. Throwing power in this bath was excellent.

Where indium sulfamate is to be supplied to the plating composition orotherwise used as such, it can be readily made by precipitation from anaqueous solution of a soluble indium salt with a strong base, thecorresponding salt of which is soluble. Thus three mols. of sodiumhydroxide may be added to a water solution of one mol. of iridiumtrichloride. Indium hydroxide precipitates and can be separated from thesodium chloride solution and then added to a solution of sulfamic acidin equivalent amount (i. e.,

three mols.) The indium sulfamate thus formed can be used directly insolution or the solution can be evaporated under vacuum, e. g. at atemperature below about 60 C. to recover the solid salt.

Although the above examples refer particularly to aqueous solutions, theinvention is applicable also to use with other ionizing solvents. Thusthe lower acid amides particularly are suitable. As one example of this20 parts by weight of sulfamic acid was dissolved in 100 parts by weightof formamide and into this was stirred 3 parts by weight indiumhydroxide. This bath, when used under ordinary plating conditions, gaveapproximately 100% cathode efficiency. Formamide is also advantageous inco-deposition of metals from sulfamate solutions, e. g. of indium andlead, zinc, silver, copper, or other non-ferrous metals.

As another example of the invention, the ingredients of the bath may bemade up in dry composition to be sold and packaged in dry form and thendissolved in a predetermined quantity of water to form the plating bath.For this purpose 45.84 grams sodium chloride, 105.36 grams indiumsulfamate, 150.00 grams sodium sulfamate, 26.40 grams sulfamic acid,8.00 grams dextrose, 2.25 grams triethanolamine or a total weight of337.85 grams of the mixture areto be dissolved in water to make oneliter of plating solution; the triethanolamine is the only liquidconstituent and can be supplied in a capsule.

For use this composition is mixed with water in proportion of 2.83 lbs.average per gallon, giving a solution of pH 1.0-1.5. This may be used asa bath for plating lead faced bearings, for example, with a pure indiumanode spaced equidistant from the bearing face and with a platingcurrent of 20 amperes per square foot of surface being plated.

As another example of the invention, indium and lead may be codepositedfrom a bath prepared as follows. An indium sulfamate bath is prepared asoutlined above, for example, containing 20 grams per liter indium and tothis is added lead sulfamate to give a concentration, for example, 0.1to 1.5 grams lead per liter. The pH ofthe bath is adjusted to 1.5 to 1.0and using an anode indium, 5% lead and a current density of 10 to 30amp. per square foot, a lead indium deposit is obtained. Of necessitythe free sulfate and chloride ions must be removed from the indiumsulfamate bath before adding the lead sulfamate. This can beaccomplished by using indium hydroxide in making the indium sulfamateand adding basic lead carbonate to precipitate the free sulfate as leadsulfate.

An anode composed of an alloy of 96% lead and 4% indium is usedcorresponding in shape to the surface to be plated so that all parts ofthe surface being plated are approximately equidistant from the nearestpart of the anode.

In this example, the anode is conformed to, and uniformly spaced from,the cathode because the throwing power of the lead is greatly inferiorto that of the indium. The throwingpower of lead can be greatly improvedby the addition of coffee extracts to the loath. Thus, in thelead-indium bath of the above example, the throwing power is increasedsufliciently to permit satisfactory use of flat anodes of lead andindium powder compressed into a plate, if dried solids of brewed roastedIcOfiee (G. Washingtons prepared coffee) are added to the bath in amountequal to about 1% to 5 grams per liter. Instead of using the coffee itis also permissible to use purified cafi'ein.

Instead of a single alloy or mixed granular anode, we may use aplurality of electrodes each of one of the metals. In general, the basicprinciples of co-deposition, as known in connection 7 withthe complexplating of-other metals inbther baths, apply here also. The sulfamateion has been found especially well adapted for such deposition.

All parts and proportions herein are by weight unless otherwisespecified.

Although certain specific examples of this invention and its applicationin practical use and also certain modifications and alternatives aregiven herein, it should be understood that these are not intended to beexhaustive or to be limiting of the invention. On the contrary, theseillustrations and the explanations herein are given in order to acquaintothers skilled in the art with this invention and the principles thereofand a suitable manner of its application in practical use, so thatothers skilled in the art may be enabled to modify the invention and -toadapt it and apply it in numerous forms, each as maybe best suited tothe requirement of a particular use.

What is claimed is:

1. An electroplating bath containing as essential electroplatingingredients the anion SOsN-Hz and the cation In in an ionizing solvent,the pH of said bath being below about 3.5, and the concentration ofindium being at least 20 grams per liter and the concentration ofsulfa-mate radical being at least 167 grams per liter.

2. An electroplating bath containing as essential electroplatingingredients the anion 'SOsNI-Iz and the cation In in an ionizingsolvent, the pH of said bath being below about 3.5, the concentration ofindium in said bath being approximately between 10 and 130 grams perliter.

3. An electroplating bath containing as -essential electroplatingingredients the anion SO3NI-I2 and the cation In in an ionizingsolvent,the pH of said bath being below about 3.5, the concentration of indiumin said bath being approximately between and 60 grams per liter.

4. An electroplating bath containing as essential electroplatingingredients the anion SOsNHz and the cation In in an ionizing solvent,the pH of said bath being below about 3.5, the concentration of indiumin said bath being approximately grams per liter, and the concentrationof the sOaNI-lz being greater than 167 grains per liter expressed as theequivalent of sulfamic acid whether present as acid, salt or 1011.

5. An electroplating bath containing as es"- sential electroplatingingredients the anion 'sOaN'Hzand the cation 'In in an ionizing solvent,

the pH-of said bath being not greater than 2.0, and the concentration ofindium being at least 20 grams per liter and the concentration ofsulfamate radical being at least 167 grams per liter.

6. The process of electrodepositing indium which comprises passing aplating current from an indium-containing anode through a bath in whichindium is the essential active cation, alkali metal is present as asecondary cation, and sulfamate is the essential active acid ion, and inwhich are also substantial but smaller amounts of an amine which formsheavy complexes with metals and maintaining the pH of said bathapproximately between 0.75 and 2.0, the concentration of indium atapproximately 30 grams per liter, and the temperature at approximatelyroom temperature.

'7. The process of electrodepositing indium by passing a plating currentthrough a cathode and an electrolytic bath in which indium is theessential active cation and the essential active anion is -SO3NH2, whilemaintaining said bath at pH below 3.5 and temperature below 80 C.

8 The process of electrodepositing indium as defined in claim 7 in whichthe concentration of indium in the bath is maintained betweenapproximately 20 and grams per liter calculated as metallic indium.

9. The process of electrodepositing indium as defined in claim 7 inwhich the bath contains lead and indium as the essential active cationsand sulfamate as the essential active anion.

J, ROBERT DYER, JR. TIMOTHY J. ROWAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 197,433 Walter Nov. 20, 18771,965,251 Murray et al July 3, 1934 2,318,592 Cupery May 11, 19432,358,029 Phillips et al Sept. 12, 1944

